www.sciencenews.org | June 23, 2018 13
a 51 percent rise in the incidence of
colorectal cancer since 1994.
Scientists aren’t sure why the disease
is increasing among younger Americans.
But it’s not just in relation to the older
group; the absolute case numbers are going up, Chan says. “The increase we are
seeing is not simply a reflection of the
drop in cancer among older groups who
are being screened.” — Aimee Cunningham
EARTH & ENVIRONMENT
As carbon dioxide increases, rice
loses B vitamins, other nutrients
By the end of this century, rice may not
deliver the same levels of B vitamins as it
does today. Protein and certain minerals
will dwindle, too, new data suggest.
Testing higher carbon dioxide concentrations in experimental rice paddies in
China predicts losses in four vitamins,
B1, B2, B5 and B9, an international team
reports May 23 in Science Advances.
Adding results from similar experiments
in Japan, the researchers also note an
average 10. 3 percent decline in protein,
an 8 percent fall in iron and a 5. 1 percent
fall in zinc, supporting previous studies of
rice and other crops (SN: 4/1/17, p. 14).
Two exceptions to losses: Vitamin B6 levels remained unchanged and vitamin E
In the experimental setups in China
and Japan, researchers grew 18 varieties
of rice. Piping exposed the rice to CO2
concentrations elevated to 568 to 590
parts per million — higher than the current level of 410 ppm, but in line with the
trend toward 570 ppm in this century.
Nine rice varieties grown in China and
tested in their unrefined brown rice form
differed in degree of vitamin loss. On
average, B1 levels (thiamine) declined
17. 1 percent; B2 levels (riboflavin), 16. 6
percent; B5 (pantothenic acid), 12. 7 per-
cent; and B9 (folate), 30. 3 percent.
Such declines could threaten the
health of those who depend heavily
on rice, now about 600 million people.
B vitamins help with a range of bodily
tasks, from maintaining a healthy brain
to enabling normal fetal development.
— Susan Milius
HUMANS & SOCIE TY
A coastal route could have led
humans into the Americas
Ancient colonizers of the Americas could
have traveled down Alaska’s Pacific coast
in canoes or other sea vessels around
17,000 years ago, a new study finds.
At that time, toward the end of the
Ice Age, glaciers had just receded from a
cluster of southern Alaskan islands, say
geologist Alia Lesnek of the University at
Buffalo in New York and colleagues. Life-supporting habitats appeared soon after
the ice melted.
The study, reported May 30 in Science
Advances, is the latest to weigh in on the
debate over how humans spread into
the New World after arriving from Asia
and reached as far as South America by
14,500 years ago. Previous work hinted
that an inland, ice-free corridor from
Alaska through what’s now British
Columbia may not have contained
enough vegetation and wildlife to enable
human travel before 12,600 years ago.
New geologic evidence supports the
coastal route idea, though Lesnek’s team
found no human bones or artifacts.
Measures of chemicals that accumu-
late in rock due to cosmic radiation once
glaciers retreat provided age estimates
for when four Alaskan islands lost
their ice coats. A pathway for coastal
travelers probably existed along the
entire southeastern Alaskan coast about
17,000 years ago, the scientists say.
Radiocarbon dates for a seal’s bones
found on a southern Alaskan island
indicate the seal lived 17,000 years ago,
suggesting the area was habitable soon
after glaciers left. — Bruce Bower
ATOM & COSMOS
Dark matter is still in hiding
The largest particle detector of its kind
has failed to find any hints of dark matter,
despite searching for about a year.
Known as XENON1T, the experiment is
designed to detect dark matter particles,
which are thought to make up most of
the matter in the cosmos. Physicists don’t
know what dark matter is. One of the
most popular explanations is a particle
called a WIMP, short for weakly interact-
ing massive particle. XENON1T searches
for WIMPs crashing into atomic nuclei in
1,300 kilograms of chilled liquid xenon.
But XENON1T saw no clear signs of such
collisions. The particles’ absence further
winnows down their possible hiding
places by placing new limits on how fre-
quently WIMPs can interact with nuclei
depending on the mass of the WIMP.
Researchers described the results
May 28 in two talks, one at Gran Sasso
National Laboratory in Italy, where
XENON1T is located, and the other at
the particle physics lab CERN near
Geneva. XENON1T had previously
reported no hint of WIMPs using about a
month’s worth of data (SN: 9/30/17,
p. 17). The new study was highly antici-
pated, as the longer search provided a
better chance for spotting WIMPs.
As the WIMP window narrows,
scientists are preparing to rev up the
search, creating more-sensitive WIMP
detectors and looking for other possible
dark matter particles, such as axions (SN
Online: 4/9/18). — Emily Conover
Extra carbon dioxide can be piped into a section of a Japanese rice paddy to simulate a future
atmosphere. Such tests suggest that rice will have lower levels of some B vitamins by 2100.